The present invention relates to a novel positive-working photoresist composition or, more particularly, to a positive-working photoresist composition capable of forming an extremely fine pattern of the resist layer even on a substrate surface having level differences or having high reflectivity of light with high resolution and sensitivity as well as with a wide range of focusing depth and a large exposure dose latitude.
The technology of photolithographic patterning by using a photoresist composition to form a patterned resist layer is well established in the manufacture of fine electronic devices including semiconductor devices such as ICs, LSIs and the like and liquid crystal display panels. The photoresist compositions most widely under practical use include those alkali-developable positive-working ones comprising an alkali-soluble resin as a film-forming ingredient and a quinone diazido group-containing compound as a photosensitive ingredient. The above mentioned alkali-soluble resin as a film-forming ingredient is typically a novolac resin which is preferred due to the good developability behavior with rapid dissolution without swelling in an alkaline aqueous developer solution and high resistance against the attack of plasma and elevated temperatures in the course of the dry-etching treatment required for a patterned resist layer as an etching mask.
The quinonediazido group-containing compound as the photosensitive ingredient is unique because the compound inherently has an activity to suppress the solubility of the novolac resin in an aqueous medium while, when exposed to actinic rays including electromagnetic waves such as ultraviolet light of so-called g-line and i-line and far-ultraviolet light such as excimer laser beams as well as corpuscular beams such as electron beams as blended with a novolac resin, the compound has an effect of promoting the solubility of the novolac resin in an alkaline medium along with the alkali-solubility imparted to the compound per se. Accordingly, a large number of positive-working photoresist compositions comprising an alkali-soluble novolac resin and a quinonediazido group-containing compound to exhibit a great change in the solubility behavior by the irradiation with actinic rays, i.e. electromagnetic waves and corpuscular beams, suitable for practical use are disclosed in, for example, U.S. Pat. No. 4,377,631, Japanese Patent Kokai No. 62-35349, No. 1-142548 and No. 1-179147, Japanese Patent Publication No. 3-4897 and elsewhere.
It is a remarkable trend in recent years in the field of the electronic industry that the degree of integration in semiconductor devices or the fineness in the patterning of liquid crystal display panels is rapidly increasing. For example, extremely fine patterning of so-called sub-micron or half-micron order or even finer is required in the manufacturing process of VLSIs which cannot be achieved without improvements in the performance of the positive-working photoresist compositions used therein. Namely, a positive-working photoresist composition is required to have high sensitivity to actinic rays from the standpoint of productivity, a wide range of focusing depth in order to give a patterned resist layer with high fidelity to the mask pattern even on a substrate surface having level differences and also to be capable of giving a patterned resist layer of high resolution and an excellently orthogonal cross sectional profile of a line pattern having good heat resistance to withstand the heat treatment (post exposure bake) before development after exposure and resistance against plasma in dry etching.
Various additives have been proposed to a positive-working photoresist composition, by which the above described requirements could be satisfied though with respective problems and disadvantages. For example, Japanese Patent Kokai No. 61-141441 discloses a positive-working photoresist composition with admixture of a trihydroxy benzophenone compound although the resist composition is poor in the heat resistance if not without improvements in the sensitivity and developability. Further, Japanese Patent Kokai No. 2-275955, No. 3-200252 and No. 3-200254 propose positive-working photosensitive compositions containing specific trisphenol-based compounds to enhance resolution, sensitivity and heat-resistance. These photoresist compositions, however, are not quite satisfactory in respect of the pattern resolution which is the most important factor in order to ensure the accuracy in the ultrafine patterning work of the resist layer.
It would be a due idea that the desired improvement in the resolution of the patterned photoresist layer could be obtained by the improvements in the exposure machine. For example, a proposal is made for the use of an exposure lens having an increased numerical aperture but an increase in the numerical aperture of a lens is necessarily accompanied by a decrease in the range of the focusing depth so that such a measure is not practical when the substrate surface has a large level difference.